1. Field of the Invention
The present invention relates to variable compression ratio (VRC) piston assemblies such as those disclosed in U.S. Pat. Nos. 3,156,162; 3,161,112; 3,185,137; 3,185,138; 3,303,831; 3,311,096; 3,402,662; 3,418,982; 3,450,111; 3,417,738; 3,417,739; 3,450,112; 3,527,265; 3,405,698; 3,405,697; 3,405,113; 3,407,791; 3,667,433; and 3,704,695; all owned by applicants' assignee and more particularly to an improved construction for such piston assemblies.
2. Description of the Prior Art
In the constructions disclosed in the patents indicated above an inner piston member is connected in the usual manner to a connecting rod and an outer piston member is carried by and is movable axially relative to the inner member. Relative movement of these members varies the compression ratio of the particular cylinder in which the piston moves. Clearance spaces are provided between the top and bottom ends of the inner and outer members and these form upper and lower chambers which vary conversely in volume in relation to the relative movement of the members. An incompressible fluid such as lubrication oil is supplied to these chambers in a manner which automatically regulates movement of the members to gradually change the compression ratio until a predetermined combustion pressure has been achieved. The hydraulic system then varies the movement of the members in a manner which tends to maintain a uniform maximum combustion chamber pressure.
In the type of assembly disclosed in these patents, inertia, oil pressure, and cylinder pressure are depended upon to provide the force for relative movement between the members and the hydraulic system is utilized to regulate the relative movement in response to changes in the fluid pressures. Inertia forces increase proportional to the square of engine speed and thus at high speeds operation of the pressure relief valve may be affected due to inertial effects on the valve parts so that it will take a greater pressure to open valves of conventional construction at high engine speeds than it will at lower engine speeds. For this reason a number of previous attempts have been made to provide such valves designed to minimize the effects of inertia upon their proper operation.
Further, in previous assemblies the lower chamber has been located in the lower skirt area of the piston necessitating substantial structure between the upper and lower chamber.
The upper chamber commonly communicates with a chamber disposed adjacent the ring area of the piston to provide cooling in this area.
Also the hydraulic systems of previous VCR assemblies have generally included a collector or supply valve assembly which directs the oil by separate passages to the upper chamber and to the lower chamber.